EASA Certification Specifiaction, part 25:
Agency Measures | Certification specifications
Due to legal status of EASA within EU, each and every document has a lot bureacratic ballast attached. Once you cut through, the document can be found, albeit not easily (I didn't find it on the site but needed to google it out):
http://www.easa.europa.eu/ws_prod/g/...ndment%206.pdf